No rational basis to think that Local's collection letter and employer's subsequent collection of full dues from employees who had requested financial core status could not be thought by a rational person to tend to restrain or coerce employees not to enforce their rights under the Act.
https://www.cadc.uscourts.gov/internet/opinions.nsf/9B76B67B9F567375852582AD0054B245/$file/16-1338-1736047.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.